Within the body, there are a total of four pulmonary veins, and all of them connect to the left atrium of the heart. The heart pumps oxygen-depleted blood into the lungs via the pulmonary arteries. Once the blood has been oxygenated, it returns to the heart via the pulmonary veins. Then, the heart circulates this newly oxygenated blood throughout the body. In this way, pulmonary veins are different from other veins in the body, which are used to carry deoxygenated blood from the rest of the body back to the heart. The left pulmonary veins connect with the left lung, and the lungs themselves are filled with hollow air sacs called alveoli. This is where oxygen is removed from inhaled air. This also works as a gas exchange. Oxygen enters the blood while carbon dioxide leaves the blood stream. This carbon dioxide is then exhaled out of the body.
